The microstructure and mechanical properties of novel Al-Cr-Fe-Mn-Ni high-entropy alloys with trimodal distributions of coherent B2 precipitates

A series of novel Co-free AlxCrFeMnNi (x = 0.5–0.8) high-entropy alloys (HEAs) with trimodal distributions of coherent B2 precipitates was fabricated. A fundamental investigation on the microstructural evolution and mechanical properties of these trimodal alloys was conducted. Structural characterization shows that these HEAs possess complex microstructures consisting of a disordered body-centered-cubic (BCC) matrix and trimodal-size distributions of the ordered coherent B2 precipitates, (1) the primary B2 (p-B2) precipitates with a mean length of ∼2 μm located in the interdendritic region, (2) the secondary B2 (s-B2) precipitates with a mean diameter of ∼450 nm, and (3) the tertiary B2 (t-B2) precipitates with a mean diameter of ∼20 nm located in the dendritic region. The trimodal HEAs exhibit a good combination of high compressive yield strengths of 1091–1200 MPa and the large plasticity (>45%). The increments of the yield strengths caused by different strengthening mechanisms have been quantitatively and respectively estimated and compared with the experimental measurements. The study of the present trimodal BCC-B2 HEAs can provide a useful guidance for the future development of multimodal BCC-based HEAs with excellent properties.